Antiphospholipid antibodies are associated with miscarriage in some autoimmune syndromes in women. The purpose of this pilot project was to establish an animal model for this problem so that possible therapies could be developed for use in humans. Affinity purified antisera to phospholipid derived from a human monoclonal antibody was obtained from collaborators. A dose of 250 5g/kg body weight was selected to achieve the 1:16 titers commonly found in women with this syndrome. Eight cynomolgous monkeys were assigned to the project after pregnancy detection. They received IV injection of the antibody at 30 day intervals beginning on day 30 gestation. The study was conducted between February and August 1995. Blood collected prior to and 1 hour after injection and urine collected 24 h before and after injection indicated that serum antibody concentrations were elevated in response to injection. Ultrasound examinations conducted at monthly intervals did not indicate a pattern of growth retardation or delayed maturation. Pregnancy outcome, including birthweight and neonatal examination, did not suggest an adverse impact of the antibody injections. We conclude that direct administration of purified human antiphospholipid antibody did not induce a pattern of fetal loss. The antibody to human phospholipids may not be active in monkeys, the administration regimen (dose and interval) may not have simulated the human fetal exposure, or the link between antibody titers and miscarriage in women may be associational rather than causal.